The Chicken has well rounded stats and useful abilities. But with only Squawk as means of defense don't expect it to avoid stuff or be very durable. Go for as much power as you can since no abilities get any extra benefits for going first.

The Eggs can really hurt undead. And if you pair it with call lightning or a damage booster like wild magic or black claw it can really shine.

As with the Yellow Moth, this pet, though purchaseable, offers a variety of breeds (4 to be exact). Considering everything, especially that flying pets enjoy a nice speed boost when over 50% health, it seems to me that the best breed for this guy would be the Breed 20 variety. Buy yourself a few of them and keep checking until you find one that features 150 health, 11 power and 10 speed at level 1 uncommon; this will translate to 1465 health, 289 power and 273 speed at 25 rare.

This pet does indeed show up as a secondary to the Scorpid. Possibly from other pets too, but I haven't seen it. Also, they all appear to be uncommon quality as I have also yet to see poor, common or rare.

But never fear, Blizz is here! They promise in patch 5.1 for battle pets to be upgradeable in some fashion. Yayyy!! No more wasting hours on a rare search when you already have an uncommon.